The prostate early in life is the size and shape of a walnut and prior to the enlargement resulting from benign prostatic hyperplasia, weighs about 20 grams. Prostate enlargement appears to be a normal process. With age, the prostate gradually increases in size to twice or more its normal size. The fibromuscular tissue of the outer prostatic capsule restricts expansion after the gland reaches a certain size. Because of such restriction on expansion, the intracapsular tissue will compress against and constrict the prostatic urethra, thus causing resistance to urine flow.
FIG. 1 is a sectional schematic view the male urogenital anatomy, with the walnut-sized prostate 100 located below the bladder 105 and bladder neck 106. The walls 108 of bladder 105 can expand and contract to cause urine flow through the urethra 110, which extends from the bladder 105, through the prostate 100 and penis 112. The portion of urethra 110 that is surrounded by the prostate 100 can be referred to as the prostatic urethra 120. The prostate 100 also surrounds the ejaculatory duct 122 which have an open termination in the prostatic urethra 120. During sexual arousal, sperm is transported from the testes 124 by the ductus deferens 126 to the prostate 100 which provides fluids that combine with sperm to form semen during ejaculation. On each side of the prostate, the ductus deferens 126 and seminal vesicles 128 join to form a single tube called an ejaculatory duct 122. Thus, each ejaculatory duct 122 carries the seminal vesicle secretions and sperm into the prostatic urethra 120. Also shown in FIG. 1 are Cowper's Gland 130, the Sigmoid Colon 132, the Rectum 134, and Epididymis 136.
Referring to FIGS. 2A-2C, the prostate can be classified into three zones: the peripheral zone, transition zone, and central zone. Peripheral zone (PZ) comprises about 70% of the volume of a male's prostate. This sub-capsular portion of the posterior aspect of the prostate gland surrounds the distal urethra and 70 to 80% of cancers originate in the peripheral zone tissue. The central zone (CZ) surrounds the ejaculatory ducts and contains about 20-25% of the prostate volume. The central zone is often the site of inflammatory processes. The transition zone (TZ) is the site in which benign prostatic hyperplasia develops, and contains about 5-10% of the volume of glandular elements in a normal prostate, but can constitute up to 80% of such volume in cases of BPH. The transition zone includes two lateral prostate lobes and the periurethral gland region. As can be understood from FIGS. 2A-2C, there are natural barriers around the transition zone, i.e., the prostatic urethra, the anterior fibromuscular stroma FS, and a fibrous plane FP between the transition zone and peripheral zone. In FIGS. 2A-2C, the anterior fibromuscular stroma FS or fibromuscular zone can be seen and is predominantly fibromuscular tissue.
Approximately 70% to 80% of prostate cancers originate in the peripheral zone of the prostate and may be confined to the peripheral zone. In recent years, there has been an increased interest in focal therapy for prostate cancer, treating only regions of tissue in which cancer has been found following biopsies. Prior art focal therapy treatments, such as with RF ablation energy, may not confine the treatment to the peripheral zone tissue.